The chief objectives of our research are to determine mechanisms by which electronic excitation energy can be degraded, stored and transferred in large organic molecules and molecular complexes. Our approach has been to use the techniques of molecular photochemistry, spectroscopy and kinetics to study phenomena in relatively simple systems of well-defined structure which have close analogies with processes occurring in vision, biochemical electron-transfer and photosynthesis. The proposed investigations include studies of the photoreactions of metalloporphyrins and their complexes, both in solution and in monolayers, investigations of the formation and reactions of excited state donor-acceptor complexes (exciplexes) in solution; and spectroscopic and photochemical studies of olefins, dienes and polyenes in oriented monolayer assemblies. (keywords for the latter area: photoreactions of oriented molecules and complexes.)